U.S. patent number 5,844,239 [Application Number 08/858,567] was granted by the patent office on 1998-12-01 for optical measuring apparatus for light scattering.
This patent grant is currently assigned to Kurashiki Boseki Kabushiki Kaisha, Kyoto Daiichi Kagaku Co., Ltd.. Invention is credited to Eiichi Kimura.
United States Patent |
5,844,239 |
Kimura |
December 1, 1998 |
Optical measuring apparatus for light scattering
Abstract
Light of a specific wavelength is introduced into respective
optical fiber members forming a light projecting optical fiber
member group (14a) through a condensing lens (26). A second end of
an optical fiber light guide path (10) whose first end is brought
into close contact with a target (20) is branched into three
optical fiber member groups including a light projecting optical
fiber member group (14a) and first and second photoreceiving
optical fiber member groups (16a, 18a), and each of the optical
fiber member groups (14a, 16a, 18a) is formed by bundling optical
fiber members forming respective unit bundles respectively. Each
unit bundle includes at least one light projecting optical fiber
member which is arranged at the center, a first photoreceiving
optical fiber member group arranged around the light projecting
optical fiber member substantially on the circumference of a first
circle concentric with the optical fiber member, and a second
photoreceiving optical fiber member group arranged substantially on
the circumference of a second circle which is concentric with the
at least one optical fiber member and larger in radius than the
first circle.
Inventors: |
Kimura; Eiichi (Osaka,
JP) |
Assignee: |
Kurashiki Boseki Kabushiki
Kaisha (Kurashiki, JP)
Kyoto Daiichi Kagaku Co., Ltd. (Kyoto, JP)
|
Family
ID: |
15723950 |
Appl.
No.: |
08/858,567 |
Filed: |
May 19, 1997 |
Foreign Application Priority Data
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May 31, 1996 [JP] |
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8-160860 |
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Current U.S.
Class: |
250/341.8;
250/341.2; 250/349 |
Current CPC
Class: |
G01N
21/474 (20130101); G02B 6/04 (20130101); A61B
5/14532 (20130101); A61B 5/1455 (20130101); G01N
2021/4747 (20130101); G01N 21/49 (20130101) |
Current International
Class: |
A61B
5/00 (20060101); G01N 21/47 (20060101); G02B
6/04 (20060101); G01N 21/49 (20060101); G01N
021/47 () |
Field of
Search: |
;250/341.8,339.07,339.08,339.1,339.11,341.1,341.2,341.7,349 |
References Cited
[Referenced By]
U.S. Patent Documents
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5596992 |
January 1997 |
Haaland et al. |
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Foreign Patent Documents
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0 627 619 |
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Dec 1994 |
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EP |
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2 361 873 |
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Jun 1974 |
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DE |
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2 115 175 |
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Sep 1983 |
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GB |
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2 304 187 |
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Mar 1997 |
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GB |
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96/41566 |
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Dec 1996 |
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WO |
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Primary Examiner: Glick; Edward J.
Assistant Examiner: Jiron; Darren M.
Attorney, Agent or Firm: Nikaido, Marmelstein, Murray &
Oram LLP
Claims
What is claimed is:
1. An optical measuring apparatus for a light scatterer comprising
a light source part generating light of infrared to near infrared
regions, a photodetection part comprising a photodetector having
sensitivity in said infrared to near infrared regions, an optical
fiber light guide path for guiding and applying said light from
said light source part to a surface of a light-scattering target,
receiving scattered/reflected light being generated from said
surface of said target and guiding the same to said photodetection
part, and a signal processor for obtaining a physical property
value in said target from a detection signal of said photodetection
part, wherein
said optical fiber light guide path comprises a plurality of unit
bundles, each unit bundle including a light projecting optical
fiber member being arranged at a center on one end surface, a first
photoreceiving optical fiber member group arranged around said
light projecting optical fiber member substantially on the
circumference of a first circle being concentric with said light
projecting optical fiber member, and a second photoreceiving
optical fiber member group arranged substantially on the
circumference of a second circle being concentric with said light
projecting optical fiber member and larger in radius than said
first circle, said unit bundles being bundled with first end
surfaces thereof flush with each other, said light projecting
optical fiber members of respective said unit bundles being bundled
and guided to said light source part on the other end surface side,
and said first photoreceiving optical fiber member groups and said
second photoreceiving optical fiber member groups of respective
said unit bundles are bundled independently of each other and
guided to said photodetection part, and
said photodetection part receives respective light components
guided by said first photoreceiving optical fiber member groups and
said second photoreceiving optical fiber member groups as different
signals.
2. The optical measuring apparatus in accordance with claim 1,
wherein
said first and second photoreceiving optical fiber member groups
are arranged in single layers, respectively.
3. The optical measuring apparatus in accordance with claim 1,
wherein
each unit bundle has respective distances between said light
projecting optical fiber member and said first photoreceiving
optical fiber member group and between said first photoreceiving
optical fiber member group and said second photoreceiving optical
fiber member group that are different from each other.
4. The optical measuring apparatus in accordance with claim 1,
wherein
diameters of said light projecting optical fiber members and
optical fiber members forming said first and second photoreceiving
fiber member groups are not identical.
5. The optical measuring apparatus in accordance with claim 1,
wherein
the number of optical fiber members forming each said second
photoreceiving optical fiber member group is larger than the number
of optical fiber members forming each said first photoreceiving
optical fiber member group.
6. The optical measuring apparatus in accordance with claim 1,
wherein
said signal processor calculates the ratio. E.sub.1 /E.sub.2
between detected intensities E.sub.1 and E.sub.2 of light
components being guided by said first and second photoreceiving
optical fiber member groups respectively in said photodetection
part, or a value -log (E.sub.2 /E.sub.1) or -logE.sub.2 /logE.sub.1
in terms of absorbance as an optically measured value, for
obtaining said physical property value of said target from a
separately obtained regression formula of said optically measured
value and a physical property value.
Description
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for measuring a
physical property value in a scatterer with light. The target
scatterer is powder, an opaque solution such as blood or cow's
milk, food such as fruit, or a human body. The powder could include
raw material for medicine or for processed food such as cornstarch
or flour, or industrial processing raw material such as ceramic.
The physical property value to be measured is moisture content or
component concentration such as protein concentration.
A method of measuring a physical property value in a scatterer is
by irradiating the target substance with light through its surface
and receiving the light scattered in and reflected by the target
substance on another point of the surface of the target substance,
thereby measuring the physical property value on the basis of data
of the received light. For example, an apparatus comprising a light
projecting end for projecting light on a target, a first
photoreceiving end for receiving scattered/reflected light in the
vicinity of the light projecting end, and a second photoreceiving
end for receiving the scattered/reflected light on a position
separated from the light projecting end for measuring a physical
property value in a deep portion of the target has been proposed
(refer to Japanese Patent Publication No. 61-11614 (1986)).
In order to improve measuring accuracy, measurement in a blank
state with no object of measurement is carried out in case of a
transmitter, while a reference scattering sample is employed for
measuring a reference spectrum in case of a scatterer. In case of
the aforementioned prior art, a signal obtained by a fiber member
shown in FIG. 14 of the reference corresponds to the reference
spectrum.
Further, measurement is made at two or three wavelengths for
obtaining ratios of data measured at different wavelengths, thereby
improving measuring accuracy.
However, the apparatus of the aforementioned prior art has the
following problems:
It refers to that measurement at a deep portion as necessary for
intracerebral measurement, and the distance between the light
projecting end and the second photoreceiving end must be at least
4.25 cm. If the light projecting end and the second photoreceiving
end are separated from each other, however, the substantial optical
path length is increased, the quantity of light reaching the second
photoreceiving end is extremely reduced due to absorbance or
scattering in a target, and the measuring accuracy is reduced.
While a fiber bundle structure is shown in FIG. 15 of the prior art
reference, a fiber member which is the second photoreceiving end is
separated from the light projecting end and hence the first and
second photoreceiving ends cannot be brought into identical bundle
structures along with the light projecting end.
Further, in the prior art reference, a fiber member serving as the
light projecting end and the fiber member serving as the second
photoreceiving end are inclinedly mounted with respect to a surface
of the target, and hence the quantity of light varies with the
depth of the target.
While projected light spreads at 360 degrees in the target, the
fiber member serving as the second photoreceiving end can receive
the light only from a partial region, with inferior
condensability.
The present invention is adapted to measure a physical property
value at a shallow region from a surface of a target. In order to
efficiently receive light projected on the target on photoreceiving
ends, a number of photoreceiving ends may be arranged around a
light projecting end. FIG. 1 shows an end surface of such an
optical fiber bundle. Plural light projecting optical fiber members
2 are arranged at the center, while first and second photoreceiving
optical fiber members 3 and 4 are arranged around the same in
multiple layers respectively.
When a number of photoreceiving ends are arranged around light
projecting ends as shown in FIG. 1, the quantity of received light
is increased for enabling optically bright measurement. However,
the photoreceiving ends are present at different distances from the
light projecting ends 2 in the first and second photoreceiving
optical fiber members 3 and 4, and a plurality of data from
portions of different depths intermix with each other to inevitably
reduce measurement accuracy.
SUMMARY OF THE INVENTION
An object of the present invention is to improve measurement
accuracy by increasing the quantity of received light while
suppressing intermixture of a plurality of data from portions of
different depths.
According to the present invention, a plurality of unit bundles are
provided with each bundle including a light projecting optical
fiber member which is arranged at the center on one end surface, a
first photoreceiving optical fiber member group arranged around the
light projecting optical fiber member substantially on the
circumference of a first circle concentric with the optical fiber
member and a second photoreceiving optical fiber member group
arranged substantially on the circumference of a second circle
which is concentric with the light projecting optical fiber member
and larger in radius than the first circle. The bundles are so
bundled that end surfaces thereof are flush with each other. The
light projecting optical fiber members of these unit bundles are
integrated with each other on the other end surfaces to be guided
to a light source part. The first photoreceiving optical fiber
member groups and the second photoreceiving optical fiber member
groups of the respective unit bundles are bundled independently of
each other to be guided to a photodetection part, so that light
components guided by the first photoreceiving optical fiber member
groups and the second photoreceiving optical fiber member groups
are received as different signals in the photodetection part.
A plurality of unit bundles are bundled, whereby the number of
optical fiber members forming the first and second photoreceiving
optical fiber member groups in the unit bundles can be reduced. It
is most preferable to arrange optical fiber members in single
layers in the first and second photoreceiving optical fiber member
groups respectively. This is most effective for suppressing
intermixture of a plurality of data from portions of different
depths. While data from the portions of different depths intermix
with each other as the thicknesses of the first and second
photoreceiving optical fiber member groups in the unit bundles are
doubly or triply increased, reduction of measurement accuracy can
be suppressed since it is not necessary to arrange the optical
fiber members in multiple layers, dissimilarly to the single
optical fiber bundle shown in FIG. 1.
Ends of the fiber members can be substantially perpendicularly
brought into close contact with the target. Light from the light
projecting optical fiber members is repeatedly scattered/reflected
in/by the target, and spreads at 360 degrees. However, the first
and second photoreceiving optical fiber member groups are
concentrically arranged around the light projecting optical fiber
members to encircle the same, whereby the respective unit bundles
can effectively receive the light. In this case, the ends of the
fiber members are substantially perpendicularly in close contact
with the target while the first and second photoreceiving optical
fiber member groups can be thinly arranged on substantially
concentric circles respectively, whereby intermixture of data from
portions of different depths can be suppressed.
The quantity of received light can be increased due to bundling of
the plurality of unit bundles. While the unit bundles are bundled,
light received by approximate optical fiber members has the
strongest intensity, and hence light from light projecting optical
fiber members of different unit bundles is relatively weak and has
only small influence.
Proper optical path lengths can be obtained by making the distances
between the light projecting optical fiber members and the first
photoreceiving optical fiber member groups and those between the
first photoreceiving optical fiber member groups and the second
photoreceiving optical fiber member groups different from each
other.
Further, the light projecting optical fiber members and the optical
fiber members forming the first and second photoreceiving optical
fiber member groups respectively can be so structured that the
diameters thereof are not the same. The overall light quantity can
be increased by thickening the light projecting optical fiber
members, for example, while the quantity of light received by the
second photoreceiving optical fiber member groups can be increased
by thickening the diameters of the optical fiber members forming
the second photoreceiving optical fiber member groups in which the
quantity of light is reduced due to long substantial optical path
lengths from light projecting points. The quantity of light
received in the second photoreceiving optical fiber member groups
can be increased also by increasing the number of the optical fiber
members forming the second photoreceiving optical fiber member
groups as compared with those forming the first photoreceiving
optical fiber member groups. Thus, the present invention can be
modified in various ways, in order to obtain an optimum quantity of
light.
According to the present invention, a plurality of unit bundles,
each including a light projecting optical fiber member arranged at
the center on one end surface, a first photoreceiving optical fiber
member group arranged around the light projecting optical fiber
member substantially on the circumference of a first circle
concentric with the optical fiber member and a second
photoreceiving optical fiber member group arranged substantially on
the circumference of a second circle which is concentric with the
light projecting optical fiber member and larger in radius than
first circle, are bundled for projecting light from the projecting
optical fiber members of the respective unit bundles on a target
while bundling the first photoreceiving optical fiber member groups
and the second photoreceiving optical fiber member groups of the
respective unit bundles independently of each other and guiding the
same to a photodetection part for detection. In this manner,
condensability is improved. Further, intermixture of data from
portions of different depths can be suppressed as compared with the
case of arranging the same number of photoreceiving optical fiber
members on multiple concentric circles in a single bundle.
Consequently, measuring accuracy is improved.
A miniature light source can be secondarily utilized so that the
apparatus itself can be miniaturized and a problem of heat
generation can be solved.
Measurement of reference light which comes into question in
scatterer measurement is rendered unnecessary, errors in reference
light measurement are eliminated, and accuracy is improved by
obtaining specific absorbance from photoreceiving signals by the
first and second photoreceiving optical fiber member groups. Due to
internal standard measurement, further, external fluctuation such
as difference between contact pressures or measured portions is
cancelled and the accuracy is improved also in this point.
Miniaturization of the apparatus itself can be attained by
employing a single interference filter as a spectroscopic part, or
utilizing an LED (light emitting diode) or an LD (laser diode)
radiating only light of a specific wavelength region as a light
source. Further, substantially no condensing optical system is
necessary, and hence miniaturization of the apparatus itself can be
attained also in this point.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing and other objects, features, aspects and advantages
of the present invention will become more apparent from the
following detailed description of the present invention when taken
in conjunction with the accompanying drawings, wherein:
FIG. 1 is an end view showing a conventional optical fiber
bundle;
FIG. 2 is an end view showing an optical fiber bundle in a first
embodiment of the present invention;
FIG. 3(A) typically illustrates optical paths in a unit bundle;
FIG. 3(B) is an end view thereof;
FIGS. 4(A) and 4(B) are end views showing other exemplary unit
bundles employed in the present invention respectively;
FIG. 5 is a schematic block diagram showing a first embodiment of
the present invention;
FIG. 6 is a schematic block diagram showing a second embodiment of
the present invention;
FIG. 7 is a schematic block diagram showing a third embodiment of
the present invention;
FIG. 8 illustrates standard deviations of spectra in case of
repeatedly measuring human brachia in example and comparative
example, respective; and
FIG. 9 illustrates correlation between blood-sugar levels in a
human body and light intensities.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 2 illustrates an end surface, which is brought into close
contact with a target, of an optical fiber light guide path 10 in
an embodiment of the present invention. This optical fiber light
guide path 10 is formed by bundling a plurality of unit bundles 12
so that respective end surfaces thereof are flush with each other
on an end surface. The unit bundles 12 are identical in structure
to each other. A light projecting optical fiber member 14 for
guiding light from a light source part and projecting the same on
the target is arranged at the center of each unit bundle 12. A
plurality of first photoreceiving optical fiber members 16 are
arranged on a substantially concentric circle around member 14, to
form a first photoreceiving optical fiber member group. On a
substantially concentric circle outside the first photoreceiving
optical fiber member group, a plurality of second photoreceiving
optical fiber members 18 are arranged to form a second
photoreceiving optical fiber member group.
FIG. 3(A) typically illustrates optical paths in each unit bundle
12, and FIG. 3(B) is an end view thereof. An end surface of each
unit bundle 12 is pressed against a target 20 to be in close
contact therewith, and thus, all of the respective optical fiber
members 14, 16 and 18 are arranged substantially perpendicularly
arranged with respect to the target 20.
Light guided from the light projecting optical fiber member 14 is
incident upon the target 20, scattered/reflected in the target 20
to be incident upon the photoreceiving optical fiber members 16 and
18, and guided to a detection part.
The first and second photoreceiving optical fiber members 14 and 16
are arranged in single layers respectively in this example, most
preferably for suppressing intermixture of a plurality of data from
portions of different depths. However, the present invention is not
restricted to the first and second photoreceiving optical fibers 14
and 16 which are arranged in single layers respectively.
FIGS. 4(A) and 4(B) illustrate other exemplary unit bundles
employed in the present invention respectively. In the example
shown in FIG. 4(A), fiber members are so arranged that distances L1
and L2 between a light projecting optical fiber member 14 and first
photoreceiving optical fiber members 16 and between the first
photoreceiving optical fiber members 16 and second photoreceiving
optical fiber members 18 are different from each other, whereby the
distances between the light projecting optical fiber member 14 and
the first and second photoreceiving optical fiber members 16 and 18
are optimumly set in response to a target and measuring
conditions.
In the example shown in FIG. 4(B), on the other hand, diameters of
optical fiber members 14, 16 and 18 are set to be different from
each other. In this example, the diameters of the light projecting
optical fiber member 14 and the second photoreceiving optical fiber
members 18 are large, and those of the first photoreceiving optical
fiber members 16 are small. The quantity of projected light can be
increased by thickening the projecting optical fiber member 14, and
the quantity of received light as well as a signal-to-noise ratio
can be increased by thickening the second optical fiber members 18
in which the quantity of received light is reduced due to a long
effective optical path length from the light projecting optical
fiber member 14.
FIGS. 5 to 7 schematically illustrate respective embodiments.
FIG. 5 illustrates a measuring apparatus employing a halogen lamp
22 generating light of multiple wavelengths as a light source and
an interference filter 24 for selecting a specific wavelength and
projecting light on a target 20. The light from the halogen lamp 22
is introduced into respective optical fiber members forming a light
projecting optical fiber member group 14a through a condenser lens
26. The interference filter 24 is arranged between the condenser
lens 26 and an incidence end of the light projecting optical fiber
member group 14a. An optical fiber light guide path 10 has an end
which is brought into close contact with the target 20 and another
end which is branched into three optical fiber member groups
including a light projecting optical fiber member group 14a and
first and second photoreceiving optical fiber member groups 16a and
18a. The light projecting optical fiber member group 14a and the
first and second photoreceiving optical fiber member groups 16a and
18a are formed by bundling the light projecting optical fiber
members 14 and the first and second photoreceiving optical fiber
members 16 and 18 of the respective unit bundles 12 shown in FIG. 2
respectively. Forward ends of the first and second photoreceiving
optical fiber member groups 16a and 18a are guided to infrared
detectors 30 and 32 respectively, for detection of the received
light. A signal processing electric circuit 34 is provided as a
signal processor, for fetching and processing detection signals
from the infrared detectors 30 and 32.
FIG. 6 illustrates a measuring apparatus which is provided with a
rotary interference filter disc 36 in place of the interference
filter 24 shown in FIG. 5, so that interference filters can be
switched by rotating the disc 36 by a stepping motor 37. A
plurality of interference filters each having different
transmission areas are arranged on the interference filter disc 36
along its circumference, so that a selected interference filter can
be arranged on an optical path between a light source 22 and an
incidence end of a light projecting optical fiber member group 14a.
Condensing optical systems 26a and 26b, which correspond to the
condenser lens 26 shown in FIG. 5 are formed by combining necessary
numbers of lenses with each other.
Each of the embodiments shown in FIGS. 5 and 6 illustrates the
so-called pre-spectroscopic system for selecting the wavelength
before projecting the light on the target, while the so-called
post-spectroscopic system of selecting a wavelength after
scattering/reflecting of the light from a target may alternatively
be employed.
FIG. 7 shows an example employing a laser diode (LD) 38 for
generating single-wavelength light as a light source. Numeral 40
denotes a driving circuit for the laser diode 38. In this case, no
filter for wavelength selection is necessary since the laser diode
38 generates single-wavelength light.
In the embodiment shown in FIG. 7, a light emitting diode (LED) may
alternatively be employed as the light source.
While the infrared detectors 30 and 32 are provided for
photoreceiving optical fiber member groups 16a and 18a
respectively, the photoreceiving optical fiber member groups 16a
and 18a may alternatively be guided to a common infrared detector
through a shutter, so that the infrared detector alternately
detects light from the photoreceiving optical fiber member groups
16a and 18a.
Results of actual measurement are now described. A halogen lamp of
30 W was employed as an infrared light source, an FTIR (Fourier
transform infrared spectrophotometer) was employed as a
spectroscopic part, and a bundle (quartz fiber member GS-180 by
Sumitomo Electric Industries, Ltd.) of 117 optical fiber members
each having a core diameter of 180 .mu.m and a clad diameter of 200
.mu.m was employed as an optical fiber light guide path 10. In this
optical fiber bundle, nineteen unit bundles 12, each comprising
nineteen optical fiber members including a light projecting optical
fiber member 14 arranged at the center, six first photoreceiving
optical fiber members 16 arranged on a substantially concentric
inner circle around the periphery of the light projecting optical
fiber member 14, and twelve second photoreceiving optical fiber
members 18 arranged on a substantially concentric outer circle as
shown in FIG. 2, were bundled for forming an optical fiber light
guide path 10. PbS detectors were employed as infrared detectors 30
and 32.
FIG. 8 shows standard deviations of spectra each obtained by
bringing a base end portion of the optical fiber light guide path
10 of such a measuring apparatus into close contact with a human
brachium and repeatedly measuring a near portion six times. The
broken line shows specific absorbance -log(E.sub.1 /E.sub.2), where
E.sub.1 and E.sub.2 represent intensities of light from first and
second photoreceiving optical fiber member groups respectively, and
the solid line shows a result of measurement with absorbance
-logE.sub.1 at a single distance from a light projecting end in
comparative example. Dispersion by the repeated measurement was
suppressed to 1/2 to 1/3 in the overall wavelength region due to
the employment of the specific absorbance, and wavelength
dependence was reduced. The dispersion is increased around 7000 to
6500 cm.sup.-1 in FIG. 8, since infrared light was almost absorbed
due to moisture absorption of the human body.
FIG. 9 shows exemplary correlation between blood-sugar levels in a
human body and light intensities expressed in specific absorbance
-log(E.sub.2 /E.sub.1) measured by employing a silicon crystal
plate as a wideband filter transmitting light of 10000 to 5400
cm.sup.-1. Excellent correlation is observed between the
blood-sugar levels and the light intensities, and it is understood
that blood-sugar levels can be optically measured by employing
specific absorbance.
Although the present invention has been described and illustrated
in detail, it is clearly understood that the same is by way of
illustration and example only and is not to be taken by way of
limitation, the spirit and scope of the present invention being
limited only by the terms of the appended claims.
* * * * *